This invention relates to the removal of ozone from air by decomposition thereof to oxygen, and is particualrly concerned with a filter for the above purpose.
Current commercial aircraft fly at altitudes where there is ozone present in the atmosphere. Recent interest in ozone removal from aircraft cabins has resulted due to an apparent increase in ozone being ingested into the passenger compartment when planes fly at altitudes as low as 23,000 feet to normal cruise altitudes of 35,000 to 39,000 feet. The ozone laden air is introduced into the aircraft cabin through the air conditioning and pressurization supply ducting. The ozone concentrations thus introduced are sufficiently high to cause some discomfort to the passengers.
To overcome this problem, recent investigations have involved the use of carbon and pelletized catalyst filters to remove the ozone under the above conditions.
Among the various ways known to eliminate ozone contamination from an ambience by decomposition of the ozone into oxygen are catalytic substances including metallic and non-metallic catalysts. Although catalytic systems appear to be the most efficient way to remove ozone from the bleed air or pneumatic ducting air supply system of an aircraft, many of such catalytic substances e.g. in the form of pellets or particles, must be carried in a container or canister, which creates problems with regard to weight as well as affecting the air flow. These materials also have other disadvantages. Thus, for example, the use of a silver coating on a metal substrate is sacrificial, in that the resultant silver oxide is readily removed and lost in the air stream. Although nickel is satisfactory it requires a very clean surface for deposition of the metal.
The following U.S. patents are exemplary of the prior art. U.S. Pat. No. 3,269,801, discloses a system for removing ozone from air, employing pellets or particles of non-metallic catalysts such as manganese dioxide located within a canister. In U.S. Pat. No. 2,980,494, it is noted that manganese dioxide when used in powder form to decompose ozone requires catalyst support pellets to prevent packing of the powder, French Pat. No. 1,436,673 discloses that ozone can be removed from air by passing the air through a layer of active granular substance, such as MnO.sub.2. However, as previously noted, such filter systems add undesirable weight to an aircraft, and also present considerable resistance to the flow of air therethrough.
U.S. Pat. No. 3,049,399 discloses that air can be deodorized by passing it through a bed of solid materials treated with potassium permanganate; U.S. Pat. No. 3,019,197 discloses a silver plated screen coated with a potassium permanganate solution which is dried and used to decompose H.sub.2 O.sub.2 ; U.S. Pat. No. 3,421,837 discloses the use of permanganate impregnated alumina for deodorizing air. In these patents, which do not relate to ozone removal, the permanganate is the active material, which is reduced to MnO.sub.2 as a result of the reaction which takes place.
It is accordingly an object of the present invention to provide an improved system for removal of ozone from air, particularly in aircraft. Another object is the provision of means for efficiently decomposing ozone in an air stream by use of a non-metallic catalyst. A particular object is the provision of a system in the form of a filter, for ozone removal from air employing a substrate containing manganese dioxide as catalyst in a non-powder or non-pellet form, the resulting system being lightweight and resistant to high temperature, and providing minimum resistance to air flow. A still further object is to provide procedure for producing such filter.